Numerous products in the high tech area include generally planar components that must be subjected to a number of sequential wet processing steps. Examples of objects processed in this manner include flat panel displays, optical and magnetic recording disks, photomasks, and silicon wafers from which semiconductor chips are fabricated. For the sake of simplicity, the present invention is discussed below with reference to the manufacture of semiconductor devices from silicon wafers. However, this is not intended to limit in any way the scope of applications to which the cassette of the present invention may be applied.
Surface processing of silicon wafers to make semiconductor devices such as integrated circuits involves a number of stages in which wafers are placed in process vessels and exposed to various fluids, such as hydrochloric acid, hydrofluoric acid, sulfuric acid, and deionized water ("DI"), a common rinse fluid. During cleaning applications in which the wafers are immersed in a cleaning solution, megasonic energy may be directed towards the wafers using one or more megasonic transducers. The resulting agitation of the cleaning solution is sufficiently powerful to remove particles from the surfaces of the wafers.
It is highly desirable to carry out such wet processing steps in vessels that promote uniform fluid flow and megasonic energy flow over the wafer surfaces, because uniform flow correlates to more uniform characteristics across the surfaces of the wafers. For environmental and cost reasons, it is further desirable to minimize the volumes of process chemicals that are consumed during processing. Also important is to minimize the amount of space the vessels and related plumbing consume within the foundry while optimizing the number of wafers that can be treated within each vessel at a given time. Doing so allows the number of wet processing stations within a given foundry to be maximized and thus increases the overall yield of the facility.